Comment # 3 on bug 64320 from Marc Dietrich

I don't see Kwin corruptions as reported in bug 64257. Also this bug says
nothing about GPU lockups. But what I also see is a "dark glxgears" effect.

It's kinda hard to bisect this because r600 now depends on llvm and different
mesa versions may require different llvm versions. I can try using the llvm
version as written in LLVM_REVISION.TXT, but that may take some time.